Powerchrom

Microdialysis was performed as described previously22 (link)46 (link). Briefly, the animals were anesthetized with sodium pentobarbital, and surgery was performed to implant a guide cannula (AG-4; EICOM, Kyoto, Japan) into the nucleus accumbens. On the following day, a dialysis probe (AI-4-1, 1-mm membrane length; EICOM) was inserted through the guide cannula and was perfused with artificial cerebrospinal fluid (148 mM NaCl, 2.7 mM KCl, 1.2 mM CaCl2, and 0.85 mM MgCl2) at a flow rate of 1 μl min–1. After an equilibration period of one hour, samples were collected every 20 minutes. After collection of at least five baseline fractions, mice were administered MAP (1 mg kg–1, i.p.), and 6 more fractions of samples were collected. The concentration of dopamine in the samples was measured by HPLC on a 4.6 by 30 mm PP-ODS column (EICOM) that was maintained at 25 °C and equipped with an electrochemical detection system (HTEC-500, EICOM) and PowerChrom (EICOM).

The 5-HT level in the dialysate sample was analyzed by an HPLC system with electrochemical detection (HPLC-ECD) (HTEC-500, Eicom Co.). A 20-μl sample was injected into an HPLC-ECD system that included an EICOMPAK CAX column (2.0 mm i.d. ×200 mm, Eicom Co.) and was set at a potential of +450 mV against a Ag/AgCl reference electrode with a graphite carbon working electrode (WE-3G, Eicom Co.). The mobile phase consisted of 0.08 M sodium sulfate-0.1 M ammonium acetate buffer (pH 6.0) containing 30% (v/v) methanol and 50 mg/l Na₂EDTA. Separations were conducted at 35°C with a flow rate of 0.25 ml/min. The standard 5-HT solution was injected every working day, and the amount of 5-HT in the samples was calculated on the basis of standard values using PowerChrom (version 2.2.4, Eicom Co.).